[Premium-Rx] The "Sound" Of Receiver IF Amplifiers

[Bob Milne]

Hi Frank & the Group,

I tend to agree with you. But I think the receivers's AGC
characteristics play a pretty important role, too. Have you ever
listened to a rapidly fading signal and notice how much extraneous
"crud" disappears when you turn off the AGC and back off on the RF
gain to the proper level? You're listening to the same filters with
the same skirts, but the dynamic response to rapidly varying signals
in very different than with the AGC on. I think this has to do with
the AGC circuit being basically a feedback (or, closed-loop, if you
prefer) circuit. And the dynamic response of this loop can have a lot
of variables that determine just how much extra "crud" is added to the
audio. And I agree that huge amounts of wideband gain after the IF
filters doesn't help matters at all.

I've seen comments about the mechanical filters in the R390A sounding
a lot harsher on static crashes than the LC filters on the older R390.
Maybe that's true. But the 51S-1 has some pretty tight mechanical
filters and they sound smooth as silk. But the 3 IF amplifiers
following the filters are all tuned-circuit amps. And the product
detector is a simple diode bridge using  IN128 diodes. Sure sounds
good, though. They even stuck in one transistor as a SSB/CW AF preamp
and it doesn't hurt that great tube sound. My biggest complaint about
the 51S-1 is that the AGC time constant is too fast for comfortable
SSB listening. But backing off on the RF gain a bit makes a big
difference.

Regards....
....Bob 

On Tue, 07 Oct 2003 08:38:33 -0400, you wrote:

>hi All,
>The sound of a receiver in my view is effected by filter skirts and IF
>amplifier gain.
<snip>